TB-IV and MSD 6 issues
 

Head scratcher of the day with the Bullet…

We got the starboard engine lit off today. Finally, some life in the old Cigarette. She ran pig rich, but my thinking is that the power valves are opening at idle (I didn’t build these carbs). I couldn’t get idle below 11-1200 with all eight screws turned pretty much shut (this is a 468 with a 250 and dual 830s). Anyway, we’ll need to dive into that more. Personally, need another set of 9022s and will be good to go. And linkage - another engineering nightmare courtesy of BDS. Again, I didn’t put this together… coming in on the back end.

Moving onto the port engine. TB-IV connected to old MSD 6. No spark. Period, Nada. Nothing. At first, we weren’t getting good contact in the barrel connector. Fixed that. Checked continuity across everything. Good. MSD has power. 12V, at wht/red distributor/module. Double-grounded at distributor and module. Wht/grn shows 4.x volts (did not move to see if it went to zero when rotor moves across pickup). Still nothing. Swapped modules. Nothing. (Interesting, we get fire on starboard engine with the port module, but timing must be whacky because it pops through blower and won’t run). Swapped to a new/backup MSD box. Nothing. I wasn’t able to force spark out of either MSD box either, but my method may have been flawed.

I want my partner to ditch all this 30+ year old stuff and move to Delco ESTs. He is adamant about keeping the MSD boxes. Cost is also an issue.

The port engine ran on the dyno with this distributor and module in place (no MSD though). What are we missing? If I can convince him to move to ESTs, can the MSD boxes be wired in? (Yes, I know they’re a crapshoot but again, he wants them).

Pulling my hair out on this one!

tap the white wire of the msd box to ground,,see if you get a spark,if so,box is good.connection in the distributor eye could be dirty and making a poor connection.

delco ests rock and are the best way to go i,ve got boxes full of failed msd and merc crap the est,s also idle better with a higher initial timing

I’ll check it out the connections and try grounding out the white wire again.

Agreed! I’d really like him to go the full EST route but he really wants the MSD boxes working. There may be some benefit to using the MSD boxes at lower engine speeds but they do nothing advantageous above 3k rpm.

the only advantage to the MSD boxes is that he will get well acquainted with the sea tow guy.

not if he sets it up w/ a few connectors,,then he can switch back over to normal TB ignition.I had a diagram on how to do it around here somewhere.

I couldn’t get spark out of either box and I know the one is definitely good. Thinking the tach may be grounding it out. I’ve asked him to disconnect it the next time he gets out to it and try again.

They’ve actually been pretty darn reliable - these are from the early 90’s if you can believe that. Guessing they were made better back then. But I agree, one day they’ll let go. A spare is on the boat.

It’s a matter of disconnecting the MSD coil wires and connecting the purple of the harness and ignition control box to the + side of the coil and the grays (ignition control box and tach) to the - side of the coil… white/red and white/green maintain their connections from the ignition box to the distributor.

I’d have to redo some of the harness to make it work plug and play. Not hard to do just need the time.